Tag Info

Hot answers tagged

32

Sure. It would happen all the time with propellers and rotors if we didn't design them to avoid it. This is something that is generally avoided in aerospace applications because the shock wave causes pretty significant drag. A lot of work goes into making sure this doesn't happen through careful selection of the blade cross section, adding sweep the ...


25

When a bell vibrates in air, it pushes air molecules out of the way which will make the vibrations "decay". If you strike a bell in vacuum, this loss mechanism will not be there so the bell will "ring" for longer (but nobody can hear it). This doesn't mean the initial amplitude is significantly greater - just that it persists longer. Obviously if you rang ...


14

It's very possible to spin something fast enough to create a sonic boom, but engineers usually try very hard to avoid it. Several aircraft have been built, on purpose, with supersonic propellers. One production aircraft is the Tupolev TU-95 Bear long-range bomber. Eight counter-rotating 4-blade props turn fast enough so the prop tips are supersonic. Rumour ...


11

I want to add to the other answers that when an object is rotating at a supersonic speed, an observer will be hit by a rapid series of sonic shock waves, as the shock wave is an ever-expanding spiral. This is what makes supersonic propellers so terribly loud. The images below depict the process. The red circle in the middle is the trajectory of a propeller ...


6

After amplification (more sound wave!) by outer hair cells in your ear, the sound wave ends up moving the flimsy bits of inner hair cells, a sensory input of your inner ear, expending some energy in the process. The rest of the energy in the sound waves also gets converted into something else, namely heat as it interacts with various parts of your ear.


4

The sound waves die down. Obviously, the sound waves, which cause a hearing sensation in our ears, cause physical movement of the eardrum and the like. but I honestly can't come up with anything that makes sense, because obviously, energy cannot be created nor destroyed. Don't worry, energy is NOT being destroyed here, it is just transferring from ...


4

Assuming a loose definition of the word "sound," the answer is yes. Let's consider the experiment you proposed. Suppose you place two large diaphragms facing each other in space. They could be simply large sheets of plastic stretched around a metal rim, like a drum head. And "large" in this context means much larger than the average distance between ...


4

The bell will not vibrate harder, but will take much longer to decay. The chief dissipation mechanisms are air, bell suspension mount, and internal friction in the metal. A well made bell's mount will be such that the fundamental vibrational mode of the bell does not produce much vibration or energy loss in the suspension point. The internal friction of a ...


4

What happens with static electricity on a shirt is, if it comes into close proximity to another surface, the difference in electrical potential can become greater than the breakdown voltage of air. Then, current flows through a small electric arc, which is a plasma of air molecules and electrons. Very locally, this has a much higher temperature than the ...


3

The ear picks up only a tiny fraction of the energy in a sound wave, but does so very effectively because of the acoustic arching mechanisms in the inner ear. The sound energy (pressure) is converted into motion of cells, and thence into heat. The amount of heat is miniscule: the sound level in a "quiet" room might be around 40 dB which corresponds to an ...


2

You just add them. There is no reason to take an average.


2

Multiply your values my some number less than 1.0. That will "move all the values closer to zero". But remember that the human hearing system is logarithmic, not linear. And "volume" is a psycho-physical phenomenon that is hard to quantify, and varies from person to person. Reducing your values by a factor of two will not reduce the perceived volume by a ...


1

When you pluck the string, you impart energy into it that's slowly radiated as sound. There are ways to radiate the energy faster, in which case the string loses energy faster. You're increasing the power and decreasing the time, so energy stays constant.


1

You need to divide by the absolute value of the maximum of the new waveform, multiplied by whatever the maximum value the sound system can handle without distortion. You need to do the absolute value because the waveform varies above and below zero, so the loudest output might be negative. So if the first waveform is wv1, the second is wv2, and the the ...


1

Speakers are designed with a combination of filters that help correct for any resonance that is provided by the enclosure. When you take the back off, you change the resonance - so you will end up with "colored" sound. Usually, it is the lower frequencies that suffer, but without details about the actual enclosure it's hard to give a definite answer. See ...


1

The answer is "yes", for speed of sound, and "maybe" for the sonic boom. It is not the speed a problem, but the apparition of different pressures along a surface or on sides of a surface and the shock waves. The extremities of the turbine inside of a vacuum cleaner can function at speeds above speed of sound if the vibrations caused by pressure are limited. ...


1

Along with your pounding heart, you're also experiencing the effects of resonance. In simple terms, there are certain frequencies of sound waves which correspond to the "natural" vibration frequency of your bones. At these frequencies, your bones vibrate with a greater amplitude than other frequencies, and you can think of it as "tapping" into the ...


1

Raphael, Active SONAR emits pressure waves that bounce off of things in the water; the timing of the pressure wave bounced back is used to measure distance and develop images of what is underwater. Given that the energy in the pressure wave dissipates at a rate defined by the inverse of the square of the distance traveled (1/r^2), it obviously takes a ...


1

Sound is a pressure wave. Continuous sound is a continuous stream of high pressure fronts followed by low pressure fronts. The louder a given sound is, the higher the difference in pressure between a crest and trough; pressure is the amplitude of the sound wave. Furthermore, the volume of a sound is also dependent on frequency. Humans are not as sensitive to ...



Only top voted, non community-wiki answers of a minimum length are eligible